The present invention relates to actuation mechanisms for mode-switching and deactivation of valves in internal combustion engines; more particularly, to such actuation mechanisms including a roller finger follower in the valve train of such an engine; and most particularly, to a system for controllably inserting and releasing an axial pin assembly in such a follower to alternately enable and prevent the roller from translating the eccentricity of a camshaft lobe into reciprocating motion of an engine valve. Such a system also may be adapted for selective switching between a low lift cam profile useful for low engine speeds and a high lift cam profile useful for high engine speeds. The low lift mode may include zero lift of the valve, i.e., deactivation thereof.
It is known to improve the fuel efficiency of multi-cylinder internal combustion engines by controllably reducing the number of combustive cylinders during periods of low power demand. Systems are known, for example, for interrupting the action of an engine""s valve train at one or more points in the engine""s rotary cycle. Valve train interruption or modulation is especially desirable because it can cause the valves of the designated cylinder or cylinders to remain closed and thus can prevent consumption of fuel by those cylinders. The valve train may be controllably interrupted, for example, by known variable mechanisms linking the camshafts to their associated roller finger followers. See, for example, the relevant disclosures of U.S. Pat. Nos. 5,937,809 and 6,019,076.
It is known that low lift, short duration cam profiles are capable of delivering good low rpm drivability, fuel economy, and emissions. High lift, long duration cam profiles are capable of providing improved engine breathing at higher engine speeds for increased power output. A valve in a valve train may be controllably switched between low lift and high lift profiles.
All such mechanisms require input from specialized sensors in the valve train to sense, for example, the angular position of a camshaft at any given moment, and sensors to sense the rotational speed of the engine. These and other inputs are provided to an Engine Control Module (ECM) programmed to respond by modulating the action of, and in the extreme deactivating or reactivating, the valves of preselected cylinders. For simply deactivating valves, such an approach can be quite complex and expensive to fabricate and install.
Another approach for interrupting the valve train is by use of special deactivatable lifters which can be made hydraulically compliant or non-compliant as desired. Such an approach can require complex and expensive hydraulic and electrical circuitry and controls.
What is needed is a simple and inexpensive means for interrupting a valve train between a camshaft lobe and a roller finger follower.
A related need is for a simple and inexpensive means for mode-switching a valve train between high lift and low lift valve actuation.
Briefly described, a mode-switching valve train system in accordance with the invention includes a specialized roller finger follower having a frame and a roller disposed operationally between a camshaft lobe and a valve stem, the follower being tethered conventionally by lash adjustment means at an end opposite the engagement point with the valve stem. A two-part axial pin for the roller is spring-loaded to urge the pin axially of the roller such that the first part of the pin is withdrawn from engagement with the follower frame and simultaneously the second part of the pin is withdrawn from the roller into an opposite side of the frame. Thus the roller becomes detached from the frame and, in following the profile of the camshaft during rotation thereof, cannot cause the frame to actuate its designated valve; thus, the valve is deactivated. When the above-described camshaft lobe is a central high lift lobe and the camshaft is additionally provided with low lift cam lobes adjacent the central lobe, the low lift lobes may engage the frame when the roller is deactivated, causing the valve to follow the profile of the low lift lobes. Thus, a roller finger follower in accordance with the invention may be used for selectively switching between valve activation and deactivation and also for selectively switching between high lift and low lift valve opening modes.
Preferably, the roller and pins are retained within the frame by at least one torsion spring. The two-part pin may be controllably reinserted into the sides of the roller and frame to reconnect the roller to the frame by the axial motion of any of various electromechanical and/or hydraulic means which may be disposed on-axis or off-axis of the two-part pin and roller.